US President-elect Joe Biden has criticised President Donald Trump’s promise of a swift coronavirus vaccine rollout, saying it has fallen behind expectations, and that if the pace wasn’t stepped up, it could take years before the bulk of Americans receive the necessary shots.

Mr Biden, speaking in Wilmington, Delaware, said some two million people have been vaccinated so far, well short of the 20 million that Mr Trump had promised by the end of the year.

At the current rate, “it’s going to take years, not months, to vaccinate the American people,” Mr Biden said.

“As I long feared and warned, the effort to distribute and administer the vaccine is not progressing as it should,” the Democrat added.

Mr Biden’s goal of ensuring that 100 million shots are administered by the end of his 100th day in office would mean “ramping up five to six times the current pace to 1 million shots a day,” he added, noting that it would require Congress to approve additional funding.

“Even with that improvement, even if we boost the speed of vaccinations to 1 million shots a day, it will still take months to have the majority of the United States’ population vaccinated,” he said.

Earlier in the day, Vice President-elect Kamala Harris received a COVID-19 vaccination live on television in a bid to boost confidence in the inoculation even while warning it will be months before it is available to all.

Senator Harris became the second high-profile person from an ethnic minority background to receive the vaccine after Surgeon General Jerome Adams on December 18.

“I want to encourage everyone to get the vaccine – it is relatively painless … it is safe … it’s literally about saving lives. I trust the scientists,” she said.

Tweet from @KamalaHarris

Mr Biden, who takes office on January 20, has said he will make the fight against the coronavirus, which has infected more than 19 million Americans and killed over 334,000, his top priority.

He received his first injected dose of the vaccine live on television last week. Two doses are required for full protection.

The Biden team has put particular emphasis on the importance of encouraging vaccine distribution and inoculation in non-white groups especially hard hit by the coronavirus.

Mr Trump, who had COVID-19 in October, frequently has played down the severity of the pandemic and overseen a response many health experts say was disorganised, cavalier and sometimes ignored the science behind disease transmission.

Mr Biden will inherit the logistical challenges of distributing the vaccine to hundreds of millions of Americans, as well as the task of persuading people who worry its development was rushed to take it.

Mr Biden and his team have warned the vaccine will take time to roll out to the general population and urged people to listen to the advice of medical experts to avoid infection by the coronavirus.

The United States has so far authorised two COVID-19 vaccines: one developed by Pfizer Inc and German partner BioNTech SE and the other by Moderna. Others are being evaluated.

Separately on Tuesday, US Senate Majority Leader Mitch McConnell put off a vote on Trump’s call to boost COVID-19 relief cheques for Americans to $2,000, in a rare challenge to his fellow Republican. Mr Biden has said he favours the increase from an already approved $600.

-AAP